The typical morphologies of Cu-doped ZnS nanocrystals in a polyvinyl alcohol (PVA) film by an ion complex transformation method observed by transmission electron microscope show that the particles were rather evenly distributed throughout the PVA film, and the dimension was estimated to be about 5.7nm in diameter. The crystallites of the ZnS have a finite bulk-like cubic structure identified by using the ED patterns of the sample. The Cu-doped ZnS UV absorption spectra are essentially similar to that of the undoped, but the luminescence properties are quite different from that of the undoped. The green emission band peaked at about 480nm is characteristic of copper doped ZnS nanocrystals, which could be attributed to a transition from the conduction band of ZnS to the 't2' level of Cu in ZnS band gap. The blue emission band peaked at about 430nm is characteristic of the undoped quantum particles of ZnS for the same size and it might be caused by the presence of self-activated centers, like zinc vacancies.